Trocars are used in medicine for making orifices and trocar port placement in body cavity walls used further for diagnostic or surgical instrument insertion into body cavity. Trocar insertion into body cavity can be accompanied with internal organ injury. To prevent such a complication, the trocars are equipped with various protectors of piercing-cutting means. However, all known solutions do not eliminate the problem of internal organ injuries.
The safety trocar penetrating instrument is known from the U.S. Pat. No. 5,591,190, comprising port unit and trocar unit with obturator having piercing-cutting means. The device is equipped with protector for piercing-cutting means made as a tubular shield situated between obturator and tubular cannula of port unit and movable relative to obturator from the extended position when it encloses piercing-cutting means and prevents it from any contact, to the retracted one, when piercing-cutting means is open and can perforate the body cavity wall. Such a protector advances to the extended position when the resistance of body cavity wall drops after the exposed piercing, cutting means has already entered the body cavity, i.e. after internal organs could have ready been injured.
Another trocar and cannula assembly are known from the U.S. Pat. No. 5,246,425, wherein a tip protector comprises a plurality of projections which, by the authors' idea should be displaced into an extended position before the piercing apex has been fully inserted into the body cavity. However, such mechanism leads to inevitable injury of body cavity wall, increased resistance to the device advance, the device advance in jerks, and high probability of protector jamming. Moreover, when these members pass through fibrous anatomical structures: aponeuroses, fascias, muscles, the structure fibers enter either the projections, or between the projections and tip. Further device advance is possible solely by rupturing these fibers which, in its turn, results in increased tissue injury and in the device hindered advance.
The tissue fibers incorporated between projections and tip can jam protector in the retracted position. In this case the jeopardy of internal body injury is even higher than by the performance of a trocar non-equipped with protector, since a surgeon, being sure of the device safety, operates with less caution.
A trocar with a shield is disclosed by U.S. Pat. No. 5,797,943. The geometry of the descried shield should, by the authors' opinion, ensure successive protection of various zones in piercing-cutting means practically simultaneously with their penetration to the body cavity.
However, shield members have such sizes, shape, arrangement and contact zone with body cavity wall that they generate considerable resistance between the shield and the body cavity wall tissues, and the latter holds the shield in totally retracted position, up to the shield complete removal beyond the bounds of body cavity wall, which means that no successive protection of piercing-cutting members takes place as they enter the body cavity.
Similar demerit is found in U.S. Pat. Nos. 5,690,663, 5,709,671. A trocar, having improved tip configuration is disclosed by U.S. Pat. No. 5,709,671, where distal edge of tubular cannula is made sloping, to facilitate the device passing through body cavity wall. In fact, the surgeon has less difficulties in trocar passing through tissues since sloping edge of cannula operates as a wedge giving the benefit of force, which facilitates tissue rupture by trocar passing. But tissue injury during the trocar performance remains considerable.